Most audio material comprises both louder and softer segments that define the material's dynamics and dynamic range. In many situations, such as listening in noisy environments or in a late-night scenario, it is desirable to reduce the dynamics and dynamic range to improve the listener experience. Several dynamic range compressors employ a time-varying gain factor to amplify soft segments and attenuate loud segments of the audio signal. When the loudness changes, the gain factor change is controlled by the compressor's attack and release time parameters. The parameters determine how fast the gain changes can be in response to increasing or decreasing loudness. The problem is that the gain change often does not match the loudness trajectory, and hence audible compressor artifacts such as “pumping” can occur.
“Pumping” artifacts are caused by a slowly rising gain factor that results in an audible loudness increase, especially in sections of the audio signal with static content. This effect cannot easily be avoided by lowering the release time parameter because a faster release can cause other modulation distortions due to the increased variations of the gain factor.
Ideally, the compression gain variations would be minimized to avoid artifacts. Hence, small loudness variations should not cause compression gain changes. Large loudness variations should only result in gain changes if loudness levels significantly change over a minimum period of time.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.